We are going to use now the Cauchy-Schwarz inequality [1]} :
\(\left(\int f\left(x \right) g\left(x \right)dx^{n}\right)^{2}\le \int f\left(x\right)^{2}dx^{n}\int g\left(x^{\prime }\right)^{2}d{x^{\prime }}^{n}.\) 
